Name: suspensions, sedimentation, and colloids
Uploaded: 2023-06-23T15:38:43.000Z
Duration: 1 min 17 s
Channel: JoVE

I colloidi e le sospensioni sono miscele eterogenee di due o più componenti fisicamente mescolati.
In un colloide, la dimensione delle particelle di soluto varia da 1 a 1000 nanometri, abbastanza piccola da essere invisibile individualmente. Tuttavia, queste particelle di soluto possono disperdere la luce, facendo apparire i colloidi traslucidi o opachi. Rimangono nella soluzione a tempo indeterminato e non si stabiliscono.
Il citosol, il materiale semifluido all'interno delle cellule viventi, è un colloide a causa delle numerose proteine e metaboliti dispersi in esso.
Al contrario, le sospensioni contengono particelle di grandi dimensioni, solitamente superiori a 10000 nanometri, spesso visibili ad occhio nudo.
Se lasciate indisturbate, queste particelle si depositano sotto forma di sedimenti.
Il sangue è un esempio di sospensione. Quando il sangue appena prelevato viene lasciato indisturbato per un po' di tempo, i globuli rossi si depositano sul fondo del contenitore. La parte liquida superiore, chiamata plasma sanguigno, è una soluzione di piccoli soluti e un colloide contenente proteine plasmatiche più grandi.

colloidi e sospensioni

I bambini durante il gioco spesso creano sospensioni come miscele di fango e acqua, farina e acqua o una sospensione di pigmenti solidi nell'acqua conosciuta come tempera. Queste sospensioni sono miscele eterogenee composte da particelle relativamente grandi visibili ad occhio nudo o con una lente d'ingrandimento. Sono torbide e le particelle sospese si depositano dopo essere state miscelate. La separazione delle particelle da una sospensione chiamata sedimentazione. Un esame del sangue per determinare la velocitdi sedimentazione misura quanto velocemente i globuli rossi in un provetta si depositano dalla porzione acquosa del sangue (chiamata plasma) in un determinato tempo. La sedimentazione rapida delle cellule del sangue di solito non avviene in un corpo sano. Tuttavia, alcuni aspetti di determinate malattie possono far aggruppare i globuli rossi e questi grumi pesanti di globuli rossi si depositano sul fondo della provetta pivelocemente delle normali cellule del sangue. Un'altra classe di miscele chiamate colloidali (o dispersioni colloidali) presenta proprietintermedie tra quelle delle sospensioni e delle soluzioni. Le particelle in un colloide sono pigrandi rispetto alla maggior parte delle molecole semplici, tuttavia le particelle colloidali sono abbastanza piccole da non depositarsi stando fermi. Le particelle in un colloide sono abbastanza grandi da diffondere la luce, un fenomeno chiamato effetto Tyndall, motivo per cui le miscele colloidali appaiono torbide o opache, come i fasci di fari. Le nuvole per esempio, sono miscele colloidali. Sono composte da goccioline d'acqua molto pigrandi delle molecole ma abbastanza piccole da non depositarsi. Alcuni colloidali hanno la proprietdi subire trasformazioni sol-gel, che possono trasformarsi reversibilmente da uno stato fluido a uno solido (gel). Ad esempio, i prodotti di gelatina si solidificano per formare un gel quando vengono refrigerati ma, possono essere liquefatti nuovamente quando riscaldati. La proprietsol-gel del citosol, il fluido delle cellule viventi, essenziale per molte attivitcellulari, come la divisione cellulare o il cambiamento di forma delle cellule. La componente particellare di una soluzione colloidale, presente in quantitrelativamente minori, chiamata fase dispersa. La sostanza o soluzione in cui distribuita la particella chiamata mezzo di dispersione. Questo testo adattato da<a href="https://openstax.org/books/anatomy-and-physiology-2e/pages/2-4-inorganic-compounds-essential-to-human-functioning">Openstax, Anatomy and Physiology 2e, Section 2.4: Inorganic Compounds Essential to Human Functioning</a> and <a href="https://openstax.org/books/chemistry-2e/pages/11-5-colloids">Openstax, Chemistry 2e, Section 11.5: Colloids</a>.

Colloidi e Sospensioni

I bambini che giocano spesso realizzano sospensioni come miscele di fango e acqua, farina e acqua, oppure una sospensione di pigmenti solidi in acqua nota come tempera...

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Colloids and Suspensions

suspensions, sedimentation, and colloids

Suspensions and colloids are two common kinds of mixtures seen in everyday life. Mud and water, flour and water, and tempera paint are suspensions. These mixtures are heterogeneous, which means their particles are not spread out evenly. The particles are relatively large and can be seen with the naked eye or a magnifying glass.

Suspension particles make mixtures cloudy, and they settle out after mixing. The settling of particles in a suspension is called sedimentation. A blood test can measure the rate of sedimentation by showing how fast red blood cells settle out of plasma, the watery part of blood, in a test tube over time. Rapid sedimentation is not usual in a healthy body, but some diseases can cause blood cells to clump together and sink faster than normal cells.

Colloids, also called colloidal dispersions, sit between suspensions and solutions. Their particles are larger than most simple molecules, but they are small enough that they do not settle out when left standing. Colloidal particles are still large enough to scatter light. This is known as the Tyndall effect, and it makes colloids look cloudy or opaque, like a beam from a searchlight.

Clouds are another example of a colloid. They contain water droplets that are bigger than molecules, but still small enough to stay suspended in the air. Some colloids can also change from a fluid sol to a solid gel and back again. Gelatin is one example. It forms a gel when chilled and can become liquid again when heated. The sol-gel behavior of cytosol, the fluid inside living cells, is important for cell division and for changes in cell shape.

In a colloid, the dispersed phase is the particulate part present in smaller amount. The dispersion medium is the substance that carries the particles throughout the mixture. These terms help describe how colloids are organized and why they behave differently from suspensions and solutions.

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Learn how suspensions settle, how sedimentation works, and why colloids stay cloudy without settling. Explore real examples like blood, clouds, and gelatin.

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Suspensions, Sedimentation, and Colloids

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